The present invention relates to a demodulator system in a facsimile and, more particularly, to a demodulator system for converting a received MH code (Modified Huffman Code) signal to an RL code (Run Length Code) signal in a facsimile system.
In a facsimile system, a transmitter forms the RL code signal in accordance with the picture information read out from an original. The RL code signal is modulated, at the transmitter, to the MH code signal which is suited for the compressed transmission, and the thus obtained MH code signal is transmitted to a receiver. The receiver includes a demodulator for converting the received MH code signal to the RL code signal, whereby the picture corresponding to the original is formed at the receiver.
The MH code signal represents the RL information of zero through 1728 bits. More specifically, when the run length is zero through 63 bits, a specific MH code is assigned to each run length. This is referred to as the terminating code. When the run length is 64 through 1728 bits, a specific MH code is assigned to each group of 64 bits. That is, a specific MH code is determined every increment of the run length by 64 bits. This is referred to as the makeup code. The terminating code and the makeup code are combined to represents the run length up to 1728 bits. For example, the black of run length=2 is represented as "11" in the MH code. The black of run length=1728 is represented as "0000001100101" in the MH code. That is, the MH code signal has bits two through thirteen.
Accordingly, the demodulator ROM must have thirteen address input bits. Therefore, the demodulator ROM must be of the capacity of 2.sup.13 =8K words. Alternatively, it is proposed to employ a plurality of PLA's (programmable logic array) which has a large number of input bits for demodulating purposes. However, this is not practical since the PLA is every expensive as compared with ROM.
Accordingly, an object of the present invention is to provide a novel demodulator system for a facsimile system.
Another object of the present invention is to provide a demodulator system for converting a received MH code signal into an RL code signal in a receiver of a facsimile system.
Still another object of the present invention is to provide a demodulator system for converting a received MH code signal into an RL code signal, which requires an ROM of a small capacity.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
In accordance with the present invention, by properly shifting the received MH code signal, the demodulator can be formed by an ROM of 2K word capacity.